iAd failed, in part, because Apple refused to provide customer details to advertisers.
>Advertisers Not Thrilled With Apple’s Practice Of Protecting Its Users’ Data... rather than offering a cookie-based ad-tracking and targeting mechanism, it essentially requires partners to tell it what kind of audience it needs to reach, and then trust that Apple will handle the rest.
>what it doesn’t do is hand over the keys to all that data and let advertisers plug into it directly with their own data-mining and targeting software. That’s not standard for the ad industry and that’s likely the reason a few Madison Avenue feathers are ruffled over their approach.
https://techcrunch.com/2014/02/18/advertisers-not-thrilled-w...
However, given recent revelations, advertising models that respect user privacy need to make a comeback.